1. Field of the Invention
The invention is based on an electro-hydraulic control device and, more particularly, to an electro-hydraulic control device for a hydraulic servo motor for controlling a volume flow, having a blocking valve arranged in a housing, whose movable seat valve body is inserted into a connection between a motor chamber and a return flow chamber for securing the motor chamber, and having a proportional magnet with an armature-actuated tappet for actuating the blocking valve.
2. Prior Art
This type of electro-hydraulic control device is already known from U.S. Pat. No. 3,667,722, by means of which a delicate proportional volume control is possible. The check valve protecting the hydraulic servo motor with its load is here designed as a pilot seat valve, so that the leakage is as small as possible. This control device can be used as a lowering brake valve, wherein the actuating forces are as low as possible and therefore the proportional magnet can be made small. It is disadvantageous in connection with this control device that only a 2/3 valve function can be represented, wherein no additional valve functions can be performed by the lowering element designed in accordance with seat valve techniques. In order to keep the actuating forces low here, a one-armed lever, with which a force transfer is performed, is placed between the proportional magnet and the actual seat valve. The force for actuating the check valve is transmitted by an unblocking member, which is made in a pin shape and with a narrow diameter, so that it cannot take on additional functions. The volume flow appearing during the lowering of a load is here only controlled by a valve cone at a seat valve body, so that the flow forces appearing particularly at high loads can considerably interfere with the proportional work functioning of the check valve. Therefore the seat valve body, which here is controlled purely hydraulically, easily tends to oscillate, particularly when pulling loads or changing load directions occur. The ball in the seat valve body, which operates as a pilot member, does not have pressure compensation. In addition, the control device is relatively elaborately constructed, to which the transmitting lever and the valve case for the check valve in particular contribute.
Furthermore, an electro-hydraulic control device had already been proposed in an older patent application, P 195 22 746.8, which operates with 4/2 valve modules. In this case two such 4/2 valve modules with additional non-return valves are arranged in a circuit in such a way that a control valve for a double-acting servo motor results. A seat valve element and a slide element are combined with each other in each 4/2 valve module in such a way, that they have a common, one-piece control member. In this not prepublished control device, this one-piece construction of the control member in the 4/2 valve module leads to a relatively elaborate construction; in addition, difficulties arise in this 4/2 valve module because of close longitudinal tolerances when adjusting the control edges to each other. Form and play tolerances are harder to control with relatively long slides in particular. Furthermore, stepped slides in stepped bores with little play make high demands in respect to deviations from running true; in addition, the stepped slides cannot be ground centerless.